Photosensitive resin composition, photosensitive element, method for forming resist pattern and method for producing printed wiring board

ABSTRACT

A photosensitive resin composition comprising: (A) a binder polymer; (B) a photopolymerizable compound that has an ethylenically unsaturated bond; and (C1) a compound represented by general formula (1) below, 
                         
wherein, at least one R represents a C 1-10  alkoxy group or a C 1-12  alkyl group; the sum of a, b, and c is 1 to 6; and when the sum of a, b, and c is 2 to 6, each R may be the same as or different from one another.

TECHNICAL FIELD

The present invention relates to a photosensitive resin composition, aphotosensitive element, a method for forming a resist pattern, and amethod for producing printed wiring boards.

BACKGROUND ART

Microelectronic circuits, as encountered with, for example, wiringboards for plasma displays, wiring boards for liquid-crystal displays,large-scale integrated circuits, thin transistors, semiconductorpackages, and so forth, are typically produced through a process knownas photolithography that involves the formation of a resist pattern. Inphotolithography, a conductor pattern is formed on a substrate, forexample, as follows. A photosensitive layer disposed on the substrate isfirst exposed to light, for example, ultraviolet radiation, through amask film bearing a prescribed pattern. A resist pattern is then formedby development with a developing solution in which the exposed regionsand unexposed regions have different solubilities. Then a conductorpattern is formed on the substrate, for example, by a plating step or anetching step, using this resist pattern as a mask.

The development of technology that enables even higher densities for thewiring of electronic circuits is being actively pursued in particular inthe surface mounting technology sector, for example, in connection withprinted wiring boards, semiconductor packages, and so forth. There isdemand in this sector that the conductor pattern constituting the wiringbe formed on the scale of 10 μm or less. The photosensitive resincomposition used in photolithography must therefore provide resolutionon the scale of 10 μm or less.

Ever higher sensitivities are also being required of the photosensitiveresin composition. Escalating wiring densities have a tendency to bringout the problem of a voltage drop due to the resistance of the powerlines. An effective response to this problem is to thicken the conductorlayer that forms the wiring to at least about 10 μm by increasing thefilm thickness of the resist pattern. Additional increases insensitivity are then required of the photosensitive resin in order to beable to form the thicker resist patterns at high productivities.

On the other hand, the procedure known as direct imaging exposure, inwhich the resist pattern is directly imaged without the use of a maskpattern, is receiving attention within the sphere of methods for formingresist patterns. Direct imaging exposure is believed to have thecapacity to form resist patterns at high resolutions and highproductivities. Moreover, the application of a long-life, high-outputgallium nitride-type blue laser light source, i.e., laser light emissionat a wavelength of 405 nm, as a practical light source has become moreand more possible in recent years. The use of such short wavelengthlaser light in direct imaging exposure is expected to make possible theformation of high density resist patterns that have heretofore beendifficult to produce. A method that applies the Digital Light Processing(DLP) system championed by Texas Instruments has been proposed by BallSemiconductor Inc., and the practical application of photoexposuredevices that use this method has already begun.

Moreover, there have already been a few disclosures with regard tophotosensitive resin compositions intended for the formation of resistpatterns by direct imaging exposure using a laser, such as the bluelaser cited above, as the active light (for example, refer to JapanesePatent Application Laid-open Nos. 2002-296764 and 2004-45596).

DISCLOSURE OF THE INVENTION

However, the existing photosensitive resin compositions are stillunsatisfactory with regard to sensitivity and resolution when employedfor the formation of high-density resist patterns by direct imagingexposure.

An object of the present invention is the introduction of aphotosensitive resin composition that enables resist pattern formationto be carried out by direct imaging exposure at a satisfactorysensitivity and a satisfactory resolution. Additional objects of thepresent invention are the introduction of a photosensitive element thatuses this photosensitive resin composition, the introduction of a methodof resist pattern formation that uses this photosensitive resincomposition, and the introduction of a method for producing printedwiring boards that uses this photosensitive resin composition.

In order to achieve these objects, the present invention provides aphotosensitive resin composition comprising: (A) a binder polymer; (B) aphotopolymerizable compound that has an ethylenically unsaturated bond;and (C1) a compound represented by general formula (1) below.

In formula (1), at least one R represents a C₁₋₁₀ alkoxy group or aC₁₋₁₂ alkyl group; the sum of a, b, and c is 1 to 6; and when the sum ofa, b, and c is 2 to 6, each R may be the same as or different from oneanother.

The photosensitive resin composition of the present invention, becauseit comprises the combination of the specific components cited above,enables resist pattern formation to be carried out by direct imagingexposure at a satisfactory sensitivity and a satisfactory resolution.The present inventors believe that these results, i.e., an improvedsensitivity and an improved resolution, are obtained due to the use of aphotopolymerization initiator comprising a pyrazoline derivative thathas specific substituents as cited for component (C1).

a, b, and c in component (C1) in the photosensitive resin composition ofthe present invention are preferably each integers from 0 to 2.

Component (A) in the photosensitive resin composition of the presentinvention preferably comprises an acrylic-type polymer that has asconstituent units thereof a monomer unit derived from acrylic acidand/or methacrylic acid and a monomer unit derived from alkyl ester ofacrylic acid and/or alkyl ester of methacrylic acid. This providesadditional improvements in the alkali developability and post-exposureresist strippability.

In addition to the preceding components, the photosensitive resincomposition of the present invention preferably further comprises, as acomponent (C2), a 2,4,5-triarylimidazole dimer or a derivative thereof.Like component (C1), this component (C2) also functions as aphotopolymerization initiator. The co-use of components (C1) and (C2) asthe photopolymerization initiator provides an additional synergisticincrease in the sensitivity and resolution and also increases theadhesiveness for substrate.

The photosensitive resin composition of the present invention preferablycontains component (B) at 20 to 80 mass parts per 100 mass parts of thetotal content of components (A) and (B) and component (C1) at 0.001 to5.0 mass parts per 100 mass parts of the total content of components (A)and (B).

When R in the compound represented by general formula (1), supra,represents a C₁₋₁₀ alkoxy group or a C₁₋₃ alkyl group, this R ispreferably a methoxy group and/or an isopropyl group and the sum of a,b, and c is preferably 1 or 2.

In addition, when R in the compound represented by general formula (1),supra, represents a C₄₋₁₂ alkyl group, this R is preferably at least onealkyl group selected from the group consisting of an n-butyl group, atert-butyl group, a tert-octyl group, and a dodecyl group. Thepyrazoline derivatives having these substituents provide a clearlysatisfactory sensitivity and resolution for the photosensitive resincomposition.

The photosensitive resin composition of the present invention ispreferably used to form a resist pattern by exposure to light having apeak in the wavelength range from at least 350 nm to less than 440 nmand particularly preferably is used to form a resist pattern by exposureto light having a peak in the wavelength range from at least 390 nm toless than 410 nm. High-density resist patterns can be easily formed by,for example, the application of direct imaging exposure using lighthaving a peak within the wavelength range from at least 350 nm to lessthan 440 nm as the active light. The photosensitive resin composition ofthe present invention is particularly useful for resist patternformation using light with these specific wavelengths.

Here, the phrase “having a peak” means that the intensity of the lightexhibits a maximum value in the prescribed wavelength range.

The component (C1) used in the photosensitive resin composition of thepresent invention preferably has a wavelength of maximum absorption offrom at least 370 nm to less than 420 nm. This “wavelength of maximumabsorption” denotes the wavelength at which the absorbance achieves itshighest value. One means for obtaining a photosensitive resincomposition suitable for the aforementioned direct imaging exposureusing the components present in conventional photosensitive resincompositions comprises simply increasing the addition of thephotopolymerization initiator in order to increase the absorbance overall wavelengths, thereby securing the sensitivity by also raising theabsorbance for light having a peak in the wavelength range from at least390 nm to less than 440 nm. However, conventional photosensitive resincompositions that contain 4,4′-bis(diethylamino)benzophenone asinitiator have a wavelength of maximum absorption around 365 nm. Due tothis, light having a peak in the wavelength range from at least 390 nmto less than 440 nm is located at the foot or fringe of the absorbancepeak (wavelength of maximum absorption: 365 nm) of such a photosensitiveresin composition. This results in a large change in sensitivity for ashift of approximately several nm in the wavelength of the irradiatedlight. On the other hand, the laser light used, for example, in directimaging exposure, exhibits a wavelength distribution to a certaindegree, and an oscillation width of approximately several nm can occurin the wavelength at the time of irradiation. Given this, the stabilityor consistency of the sensitivity will tend to be reduced in those caseswhere nothing more than a simple increase in the addition of thephotopolymerization initiator has been carried out.

However, because the wavelength of maximum absorption of component (C1)lies from at least 370 nm to less than 420 nm, the photosensitive resincomposition of the present invention as described above, when subjectedto exposure by light having a peak in the wavelength range from at least350 nm to less than 440 nm, is able to thoroughly inhibit the changes insensitivity that occur even when the wavelength of the absorbed lightshifts by approximately several nm. This enables a substantially betterresponse even in the face of shifts of approximately several nm in thewavelength of the irradiated light.

When the wavelength of maximum absorption by component (C1) is less than370 nm, the sensitivity for light having a peak in the wavelength rangefrom at least 390 nm to less than 440 nm (for example, laser light at405 nm) tends to decline, and when the wavelength of maximum absorptionis 420 nm or more, the stability under yellow light ambients tends todecline.

The present invention provides a photosensitive element comprising asupport and a photosensitive layer that is disposed on said support andthat comprises the hereinabove-described photosensitive resincomposition of the present invention. This photosensitive element,because it has the hereinabove-described photosensitive resincomposition of the present invention disposed on it as a photosensitivelayer, can carry out resist pattern formation by direct imaging exposureat a satisfactory sensitivity and a satisfactory resolution. Thisphotosensitive element is therefore well qualified, for example, for theproduction of a printed wiring board that carries a high-density wiringpattern.

The present invention provides a method of forming a resist pattern,comprising: a photosensitive layer forming step of forming aphotosensitive layer comprising the above-described photosensitive resincomposition on a substrate; an exposing step of exposing prescribedregions of the photosensitive layer to light that has a peak in thewavelength range from at least 350 nm to less than 440 nm; and adeveloping step of developing the exposed photosensitive layer to form aresist pattern. The present invention also provides a method ofproducing a printed wiring board, comprising the steps cited above and aconductor pattern forming step of forming a conductor pattern on thesubstrate based on the resist pattern that has been formed.

The method of the present invention for forming a resist patternpreferably comprises: a photosensitive layer forming step of forming aphotosensitive layer comprising the above-described photosensitive resincomposition on a substrate; an exposing step of exposing prescribedregions of the photosensitive layer to light that has a peak in thewavelength range from at least 350 nm to less than 440 nm; and adeveloping step of developing the exposed photosensitive layer to form aresist pattern. The present invention also provides a method ofproducing a printed wiring board, comprising the steps cited above and aconductor pattern forming step of forming a conductor pattern on thesubstrate based on the resist pattern that has been formed.

The above-described method for forming a resist pattern and theabove-described method of producing a printed wiring board, because theyemploy the photosensitive resin composition of the present invention,are able to produce a high-density resist pattern or conductor patternon a substrate at high productivities.

The present invention provides a photosensitive resin composition thatenables resist pattern formation to be carried out by direct imagingexposure at a satisfactory sensitivity and a satisfactory resolution.The present invention also provides a photosensitive element that usesthis photosensitive resin composition, a method of resist patternformation that uses this photosensitive resin composition, and a methodfor producing printed wiring boards that uses this photosensitive resincomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the photosensitive element according tothe present invention in schematic cross section.

FIG. 2 shows the UV absorption spectra of photosensitive layers inaccordance with examples of the present invention.

FIG. 3 shows the UV absorption spectra of photosensitive layers inaccordance with examples of the present invention.

FIG. 4 shows the UV absorption spectra of photosensitive layers inaccordance with examples of the present invention.

FIG. 5 shows the UV absorption spectra of photosensitive layers inaccordance with examples of the present invention and comparativeexamples.

FIG. 6 shows the UV absorption spectra of photosensitive layers inaccordance with examples of the present invention and comparativeexamples.

DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   1 . . . photosensitive element    -   10 . . . support    -   14 . . . photosensitive layer

BEST MODE FOR CARRYING OUT THE INVENTION

Suitable embodiments of the present invention are described in detailhereinbelow, as necessary with reference to the figures. The samereference symbols are assigned to the same elements throughout thefigures and redundant descriptions have been omitted. Positionalrelationships, such as top and bottom, left and right, and so forth, arebased on the positional relationships shown in the figures, unlessstated otherwise. In addition, the dimensional ratios depicted in thefigures are not limited to the graphically represented ratios. In thisDescription, “(meth)acrylic acid” denotes “acrylic acid” and the“methacrylic acid” corresponding thereto; “(meth)acrylate” denotes“acrylate” and the “methacrylate” corresponding thereto; the“(meth)acryloxy group” denotes the “acryloxy group” and the“methacryloxy group” corresponding thereto; and the “(meth)acryloylgroup” denotes the “acryloyl group” and the “methacryloyl group”corresponding thereto.

The photosensitive resin composition of the present embodiment comprises(A) a binder polymer, (B) a photopolymerizable compound that contains anethylenically unsaturated bond, and (C1) a pyrazoline derivative asrepresented by the preceding general formula (1).

There are no particular limitations on the component (A) binder polymeras long as it is a polymer that enables the uniform dissolution ordispersion of the other components of the resin composition. Component(A) can be exemplified by acrylic-type resins, styrenic resins,epoxy-type resins, amide-type resins, amidoepoxy-type resins, alkyd-typeresins, phenolic resins, and so forth. A single one of these may be usedas component (A) or two or more may be used in combination as component(A). Among these, the presence of an acrylic-type polymer in component(A) is preferred from the standpoint of obtaining an excellent alkalidevelopability and an excellent resist strippability after irradiationwith light. This acrylic-type polymer more preferably contains asconstituent units thereof both a monomer unit derived from acrylic acidand/or methacrylic acid and a monomer unit derived from alkyl acrylatesand/or alkyl methacrylates. Here, “acrylic-type polymer” denotes apolymer that contains primarily monomer units derived from (meth)acrylicgroup-containing polymerizable monomer.

The aforementioned acrylic-type polymer may be produced, for example, bythe radical polymerization of (meth)acrylic group-containingpolymerizable monomer. This (meth)acrylic group-containing polymerizablemonomer can be exemplified by acrylamide, acrylonitrile, alkyl(meth)acrylates, tetrahydrofurfuryl (meth)acrylate, dimethylaminoethyl(meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl(meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate,2,2,3,3-tetrafluoropropyl (meth)acrylate, (meth)acrylic acid,α-bromo(meth)acrylic acid, α-chloro(meth)acrylic acid,β-furyl(meth)acrylic acid, β-styryl(meth)acrylic acid, and so forth. Asingle one of these may be employed as the polymerizable monomer or twoor more may be used in combination as the polymerizable monomer. Thealkyl (meth)acrylates cited above can be exemplified by methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl(meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, andstructural isomers of the preceding. A single one of these polymerizablemonomers may be used or two or more can be used in combination.

In addition to the (meth)acrylic group-containing polymerizable monomercited above, a single polymerizable monomer or two or more polymerizablemonomers, as exemplified by styrene, polymerizable styrene derivativese.g., vinyltoluene, α-methylstyrene, p-methylstyrene, p-ethylstyrene,and so forth, esters of vinyl alcohol such as vinyl n-butyl ether,maleic acid, maleic anhydride, maleate monoesters e.g., monomethylmaleate, monoethyl maleate, monoisopropyl maleate and so forth, fumaricacid, cinnamic acid, α-cyanocinnamic acid, itaconic acid, crotonic acid,propionic acid, and so forth, may also be copolymerized in theacrylic-type polymer.

The binder polymer preferably contains the carboxyl group in order toprovide binder polymer that has a particularly good alkalidevelopability. This carboxyl group-containing binder polymer can beexemplified by the acrylic-type polymer described above that has acarboxyl group-containing polymerizable monomer (preferably methacrylicacid) as a monomer unit.

When the binder polymer contains the carboxyl group, its acid number ispreferably 30 to 200 mg KOH/g and more preferably is 45 to 150 mg KOH/g.The developing time tends to grow longer when the acid number is lessthan 30 mg KOH/g; the post-exposure resistance of the photocuredphotosensitive layer to the developing solution tends to decline whenthe acid number exceeds 200 mg KOH/g.

The binder polymer preferably contains styrene or a styrene derivativeas a monomer unit from the standpoint of obtaining binder polymer thatexhibits both an excellent adhesiveness and excellent strippingcharacteristics. The binder polymer preferably contains, with referenceto the binder polymer as a whole, from 3 to 30 mass %, more preferablyfrom 4 to 28 mass %, and even more preferably 5 to 27 mass % styrene orstyrene derivative. The adhesiveness tends to deteriorate when thiscontent is less than 3 mass % and there is a tendency for the strippedfragments to be large and for the stripping time to lengthen when thiscontent exceeds 30 mass %. A preferred example of binder polymer havingstyrene or a styrene derivative as a monomer unit is the acrylic-typepolymer described above in which styrene or a styrene derivative iscopolymerized along with (meth)acrylic group-containing polymerizablemonomer.

The binder polymer may as necessary also have a photosensitive group,for example, an ethylenically unsaturated bond.

The binder polymer has a dispersity (weight-average molecularweight/number average molecular weight) preferably of 1.0 to 3.0 andmore preferably of 1.0 to 2.0. The adhesiveness and resolution tend todecline when the dispersity exceeds 3.0. The weight-average molecularweight and number-average molecular weight are measured in thisembodiment by gel permeation chromatography (GPC) and are the valuesbased on the use of polystyrene standards as the calibrating standards.

The weight-average molecular weight (value measured by gel permeationchromatography (GPC) based on polystyrene standards) of the binderpolymer is preferably 5000 to 300000, more preferably 40000 to 150000,and particularly preferably 45000 to 80000. The resistance to thedeveloping solution tends to decline when the number-average molecularweight is less than 5000, while the developing time tends to lengthenwhen the number-average molecular weight exceeds 300000.

The binder polymer may be constituted of only a single polymer or may beconstituted of a combination of two or more polymers. Combinations oftwo or more polymers can be exemplified by combinations of two or morecopolymers that contain different copolymerized components, combinationsof two or more polymers that have different weight-average molecularweights, combinations of two or more polymers that have differentdispersities, and so forth. Polymer having a multimode molecular weightdistribution, as described in Japanese Patent Application Laid-open No.H 11-327137, can also be used as the binder polymer.

The blending proportion of the component (A) binder polymer in thephotosensitive resin composition is preferably 20 to 80 mass parts, morepreferably 30 to 70 mass parts, and even more preferably 40 to 60 massparts, in each case per 100 mass parts of the total of component (A) andthe component (B) described below. When this blending proportion is lessthan 20 mass parts, the region cured by photoexposure of thephotosensitive resin composition layer comprising the photosensitiveresin composition is more readily susceptible to embrittlement than whenthis blending proportion is within the aforementioned range; thecoatability also tends to be inferior in the case of application as aphotosensitive element. The photosensitivity tends to be unsatisfactorywhen this blending proportion exceeds 80 mass parts as compared to ablending proportion in the aforementioned range.

Component (B), a photopolymerizable compound that has an ethylenicallyunsaturated bond, may be any photopolymerizable compound that containsat least one ethylenically unsaturated bond. In particular, thecombination of a monofunctional photopolymerizable compound that has oneethylenically unsaturated bond with a multifunctional photopolymerizablecompound that has at least two ethylenically unsaturated bonds ispreferably used as component (B).

The ethylenically unsaturated bond carried by component (B) is notparticularly restricted as long as it is photopolymerizable and can beexemplified by α,β-unsaturated carbonyl groups such as the(meth)acrylate group and so forth. Photopolymerizable compounds thathave an α,β-unsaturated carbonyl group as the ethylenically unsaturatedbond can be exemplified by the α,β-unsaturated carboxylic acid esters ofpolyvalent alcohols, (meth)acrylate compounds that contain the bisphenolA skeleton, adducts between glycidyl-functional compounds andα,β-unsaturated carboxylic acids, urethane bond-containing(meth)acrylate compounds, nonylphenoxypolyethyleneoxyacrylates,(meth)acrylate compounds that contain the phthalic acid skeleton, alkyl(meth)acrylate esters, and so forth. A single one of these may be usedor two or more of these may be used in combination. Viewed from theperspective of the adhesiveness and resistance to plating, preferredthereamong are (meth)acrylate compounds that contain the bisphenol Askeleton and urethane bond-containing (meth)acrylate compounds wherein(meth)acrylate compounds that contain the bisphenol A skeleton areparticularly preferred.

The esters of polyvalent alcohols with α,β-unsaturated carboxylic acidscan be exemplified by polyethylene glycol di(meth)acrylates that havefrom 2 to 14 ethylene groups, polypropylene glycol di(meth)acrylatesthat have from 2 to 14 propylene groups, polyethylene.polypropyleneglycol di(meth)acrylates that have from 2 to 14 ethylene groups and from2 to 14 propylene groups, trimethylolpropane di(meth)acrylate,trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropanetri(meth)acrylate, PO-modified trimethylolpropane tri(meth)acrylate,EO-+PO-modified trimethylolpropane tri(meth)acrylate,tetramethylolmethane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, and so forth. A single one ofthese may be used or two or more may be used in combination. With regardto the preceding compound names, “EO-modified” indicates a compound thathas a block structure formed by the ethylene oxide group, while“PO-modified” indicates a compound that has a block structure formed bythe propylene oxide group.

The (meth)acrylate compound that contains the bisphenol skeleton is notparticularly limited as long as it contains the bisphenol A skeleton(the structure yielded by removing the hydrogen atoms from the twophenolic hydroxyl groups of bisphenol A) and contains the methacrylategroup or the acrylate group or both the methacrylate group and theacrylate group. Specific examples are2,2-bis(4-((meth)acryloxypolyethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypolypropoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypolybutoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypolyethoxypolypropoxy)phenyl)propane, and soforth.

The 2,2-bis(4-((meth)acryloxypolyethoxy)phenyl)propane preferablycontains from 4 to 20 ethylene oxide groups and more preferably containsfrom 8 to 15 ethylene oxide groups. The2,2-bis(4-((meth)acryloxypolyethoxy)phenyl)propane can be specificallyexemplified by 2,2-bis(4-((meth)acryloxydiethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytriethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytetraethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypentaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyhexaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyheptaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyoctaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxynonaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxydecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyundecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxydodecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytridecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxytetradecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxypentadecaethoxy)phenyl)propane,2,2-bis(4-((meth)acryloxyhexadecaethoxy)phenyl)propane, and so forth.

Among the preceding compounds,2,2-bis(4-(methacryloxypentaethoxy)phenyl)propane can be acquiredcommercially as “BPE-500” (product name, Shin-nakamura Chemical Co.,Ltd.). In addition,2,2-bis(4-(methacryloxypentadecaethoxy)phenyl)propane can be acquiredcommercially as “BPE-1300” (product name, Shin-nakamura Chemical Co.,Ltd.).

The urethane bond-containing (meth)acrylate compounds can be exemplifiedby the adducts of (meth)acrylic monomer having OH in the β-position witha diisocyanate compound (e.g., isophorone diisocyanate, 2,6-toluenediisocyanate, 2,4-toluene diisocyanate, 1,6-hexamethylene diisocyanate,and so forth), and by tris((meth)acryloxytetraethylene glycolisocyanate)hexamethylene isocyanurate, EO-modified urethanedi(meth)acrylate, EO-+PO-modified urethane di(meth)acrylate, and soforth. “UA-11” (product name, Shin-nakamura Chemical Co., Ltd.) is anexample of a commercially available EO-modified urethanedi(meth)acrylate. “UA-13” (product name, Shin-nakamura Chemical Co.,Ltd.) is an example of a commercially available EO-+PO-modified urethanedi(meth)acrylate. A single one of these can be used or two or more canbe used in combination.

The nonylphenoxypolyethyleneoxyacrylate can be exemplified bynonylphenoxytetraethyleneoxyacrylate,nonylphenoxypentaethyleneoxyacrylate,nonylphenoxyhexaethyleneoxyacrylate,nonylphenoxyheptaethyleneoxyacrylate,nonylphenoxyoctaethyleneoxyacrylate,nonylphenoxynonaethyleneoxyacrylate,nonylphenoxydecaethyleneoxyacrylate, andnonylphenoxyundecaethyleneoxyacrylate. A single one of these can be usedor two or more can be used in combination.

The above-cited (meth)acrylate compound that contains the phthalic acidskeleton is not particularly limited as long as it contains the phthalicacid skeleton (the structure given by removing the hydrogen atoms fromthe two carboxyl groups of phthalic acid) and contains the methacrylategroup or the acrylate group or both the methacrylate group and theacrylate group. Specific examples thereof areγ-chloro-α-hydroxypropyl-β′-(meth)acryloyloxyethyl-o-phthalate,β-hydroxyalkyl-β′-(meth)acryloyloxyalkyl-o-phthalate, and so forth.

The blending proportion for the component (B) photopolymerizablecompound that has an ethylenically unsaturated bond is preferably 20 to80 mass parts, more preferably 30 to 70 mass parts, and even morepreferably 40 to 60 mass parts, in each case per 100 mass parts of thetotal of components (A) and (B). When this blending proportion is lessthan 20 mass parts, the photosensitivity tends to be unsatisfactory ascompared to a blending proportion within the aforementioned range andwhen this blending proportion exceeds 80 mass parts, the photocuredregions tend to be more susceptible to embrittlement than when thisblending proportion is within the aforementioned range.

The pyrazoline derivative comprising component (C1) is represented bygeneral formula (1), supra, but is not otherwise particularly limited.In formula (1), at least one R represents C₁₋₁₀ alkoxy or C₁₋₁₂ alkyl;the sum of a, b, and c is 1 to 6; and when the sum of a, b, and c is 2to 6, each R may be the same as or different from one another.

The R's in component (C1) may be straight chain or may be branched. Rcan be exemplified by methoxy, isopropyl, n-butyl, tert-butyl,tert-octyl, and dodecyl, but is not limited to the preceding. The sum ofa, b, and c in general formula (1) is preferably 1 to 6, more preferably1 to 4, and particularly preferably 1 or 2.

From the perspective of bringing about additional improvements in thesensitivity and solubility, pyrazoline derivatives are preferred withinthe range available to component (C1) in which R is C₁₋₁₀ alkoxy or C₁₋₃alkyl. Moreover,1-phenyl-3-(4-methoxystyryl)-5-(4-methoxyphenyl)-pyrazoline isparticularly preferred from the perspective of ease of synthesis andbringing about an increased sensitivity, while1-phenyl-3-(4-isopropylstyryl)-5-(4-isopropylphenyl)-pyrazoline isparticularly preferred from the perspective of ease of synthesis andbringing about an additional increase in solubility.

From the standpoint of more reliably obtaining a satisfactoryphotosensitivity and resolution when the photosensitive resincomposition of the present invention is used in direct imaging exposure,the wavelength of maximum absorption for component (C1) is preferablyfrom at least 370 nm to less than 420 nm and more preferably is from atleast 380 nm to less than 400 nm.

The pyrazoline derivative (C1) can be exemplified by1-(4-methoxyphenyl)-3-styryl-5-phenylpyrazoline,1-phenyl-3-(4-methoxystyryl)-5-(4-methoxyphenyl)pyrazoline,1,5-bis-(4-methoxyphenyl)-3-(4-methoxystyryl)pyrazoline,1-(4-isopropylphenyl)-3-styryl-5-phenylpyrazoline,1-phenyl-3-(4-isopropylstyryl)-5-(4-isopropylphenyl)pyrazoline,1,5-bis-(4-isopropylphenyl)-3-(4-isopropylstyryl)pyrazoline,1-(4-methoxyphenyl)-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(4-methoxystyryl)-5-(4-methoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(4-isopropylstyryl)-5-(4-isopropylphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(4-isopropylstyryl)-5-(4-isopropylphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(4-methoxystyryl)-5-(4-methoxyphenyl)pyrazoline,1-phenyl-3-(3,5-dimethoxystyryl)-5-(3,5-dimethoxyphenyl)pyrazoline,1-phenyl-3-(3,4-dimethoxystyryl)-5-(3,4-dimethoxyphenyl)pyrazoline,1-phenyl-3-(2,6-dimethoxystyryl)-5-(2,6-dimethoxyphenyl)pyrazoline,1-phenyl-3-(2,5-dimethoxystyryl)-5-(2,5-dimethoxyphenyl)pyrazoline,1-phenyl-3-(2,3-dimethoxystyryl)-5-(2,3-dimethoxyphenyl)pyrazoline,1-phenyl-3-(2,4-dimethoxystyryl)-5-(2,4-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(3,5-dimethoxystyryl)-5-(3,5-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(3,4-dimethoxystryl)-5-(3,4-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(2,6-dimethoxystyryl)-5-(2,6-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(2,5-dimethoxystyryl)-5-(2,5-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(2,3-dimethoxystyryl)-5-(2,3-dimethoxyphenyl)pyrazoline,1-(4-methoxyphenyl)-3-(2,4-dimethoxystyryl)-5-(2,4-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(3,5-dimethoxystyryl)-5-(3,5-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(3,4-dimethoxystyryl)-5-(3,4-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(2,6-dimethoxystyryl)-5-(2,6-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(2,5-dimethoxystyryl)-5-(2,5-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(2,3-dimethoxystyryl)-5-(2,3-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(2,4-dimethoxystyryl)-5-(2,4-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(3,5-dimethoxystyryl)-5-(3,5-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(3,4-dimethoxystyryl)-5-(3,4-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(2,6-dimethoxystyryl)-5-(2,6-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(2,5-dimethoxystyryl)-5-(2,5-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(2,3-dimethoxystyryl)-5-(2,3-dimethoxyphenyl)pyrazoline,1-(4-isopropylphenyl)-3-(2,4-dimethoxystyryl)-5-(2,4-dimethoxyphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-styryl-5-phenylpyrazoline,1-phenyl-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline,1,5-bis(4-tert-butylphenyl)-3-(4-tert-butylstyryl)pyrazoline,1-(4-tert-octylphenyl)-3-styryl-5-phenylpyrazoline,1-phenyl-3-(4-tert-octylstyryl)-5-(4-tert-octylphenyl)pyrazoline,1,5-bis(4-tert-octylphenyl)-3-(4-tert-octylstyryl)pyrazoline,1-(4-dodecylphenyl)-3-styryl-5-phenylpyrazoline,1-phenyl-3-(4-dodecylstyryl)-5-(4-dodecylphenyl)pyrazoline,1-(4-dodecylphenyl)-3-(4-dodecylstyryl)-5-(4-dodecylphenyl)pyrazoline,1-(4-tert-octylphenyl)-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline,1-(4-tert-butylphenyl)-3-(4-tert-octylstyryl)-5-(4-tert-octylphenyl)pyrazoline,1-(4-dodecylphenyl)-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline,1-(4-tertbutylphenyl)-3-(4-dodecylstyryl)-5-(4-dodecylphenyl)pyrazoline,1-(4-dodecylphenyl)-3-(4-tert-octylstyryl)-5-(4-tert-octylphenyl)pyrazoline,1-(4-tert-octylphenyl)-3-(4-dodecylstyryl)-5-(4-dodecylphenyl)pyrazoline,1-(2,4-di-n-butylphenyl)-3-(4-dodecylstyryl)-5-(4-dodecylphenyl)pyrazoline,1-phenyl-3-(3,5-di-tert-butylstyryl)-5-(3,5-di-tert-butylphenyl)pyrazoline,1-phenyl-3-(2,6-di-tert-butylstyryl)-5-(2,6-di-tert-butylphenyl)pyrazoline,1-phenyl-3-(2,5-di-tert-butylstyryl)-5-(2,5-di-tert-butylphenyl)pyrazoline,1-phenyl-3-(2,6-di-n-butylstyryl)-5-(2,6-di-n-butylphenyl)pyrazoline,1-(3,4-di-tert-butylphenyl)-3-styryl-5-phenylpyrazoline,1-(3,5-di-tert-butylphenyl)-3-styryl-5-phenylpyrazoline,1-(4-tert-butylphenyl)-3-(3,5-di-tert-butylstyryl)-5-(3,5-di-tert-butylphenyl)pyrazoline,and1-(3,5-di-tert-butylphenyl)-3-(3,5-di-tert-butylstyryl)-5-(3,5-di-tert-butylphenyl)pyrazoline.

A single component (C1) may be used or two or more components (C1) maybe used in combination.

The blending proportion for component (C1) is preferably 0.001 to 5.0mass parts, more preferably 0.05 to 0.8 mass part, even more preferably0.01 to 2.0 mass parts, particularly preferably 0.1 to 0.5 mass part,and very preferably 0.2 to 0.4 mass part, in each case per 100 massparts of the total of components (A) and (B). Achieving both asatisfactory photosensitivity and a satisfactory resolution tends to bemore problematic when the component (C1) blending proportion is outsidethe range cited above than when this blending proportion is within thecited range.

The pyrazoline derivative comprising the component (C1) of the presentinvention can be synthesized by known methods. For example, thispyrazoline derivative can be obtained by the synthetic method describedin Japanese Granted Patent Number 2,931,693 or by synthetic methodsbased thereon. For example, a specific benzaldehyde can first becondensed by a known condensation method with acetone or a specificacetophenone compound in the presence of a base in a water-alcohol mixedsolvent. Or, a specific benzaldehyde compound and a specificacetophenone compound can be condensed in an organic solvent in thepresence of a base catalyst, for example, piperidine. The chalconecompound yielded by these condensations can then be condensed by a knownmethod with a specific hydrazine compound, for example, by reaction inacetic acid or an alcohol, to obtain the pyrazoline derivative accordingto the present invention.

The pyrazoline derivative comprising component (C1) of the presentinvention may also be acquired by purchase.1-Phenyl-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline (NipponChemical Works Co., Ltd.) is a commercially available component (C1).

The present inventors consider the co-use of the pyrazoline derivativecomprising component (C1) with the other components to be one of themain factors that make it possible for the photosensitive resincomposition of the present embodiment to achieve a satisfactorily highphotosensitivity and resolution in direct imaging exposure.

Based on considerations of adhesiveness and sensitivity, thephotosensitive resin composition of the present embodiment morepreferably additionally contains a 2,4,5-triarylimidazole dimer orderivative thereof component (C2) as a photopolymerization initiator inaddition to component (C1). The use of the abovementioned component (C2)is effective to further enhance photosensitivity and resolution.

The 2,4,5-triarylimidazole dimer can be specifically exemplified by2-(o-chlorophenyl)-4,5-diphenylimidazole dimer,2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer,2-(o-fluorophenyl)-4,5-diphenylimidazole dimer,2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer,2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer, and so forth. A singleone of these or two or more of these in combination can be used ascomponent (C2).

The blending proportion for the 2,4,5-triarylimidazole dimer orderivative thereof comprising component (C2) is preferably 0.1 to 20mass parts, more preferably 0.5 to 10 mass parts, even more preferably 1to 5 mass parts, and particularly preferably 3 to 5 mass parts, in eachcase per 100 mass parts of the total of components (A) and (B).Achieving the effects cited above for the addition of component (C2) toa satisfactory degree tends to be problematic when this blendingproportion is less than 0.1 mass part, while exceeding 20 mass partstends to impair the effects of the other components.

The following photopolymerization initiators may also be added to thephotosensitive resin composition on an optional basis in addition tocomponents (C1) and (C2): coumarin derivatives; benzophenone;N,N′-tetraalkyl-4,4′-diaminobenzophenones such asN,N′-tetramethyl-4,4′-diaminobenzophenone (Michler's ketone),N,N′-tetraethyl-4,4′-diaminobenzophenone, and so forth; aromatic ketonessuch as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1-one,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and soforth; quinones such as alkylanthraquinones and so forth; benzoin ethercompounds such as benzoin alkyl ethers and so forth; benzoin compoundssuch as benzoin, alkylbenzoins, and so forth; benzil derivatives such asbenzil dimethyl ketone and so forth; acridine derivatives such as9-phenylacridine, 1,7-bis(9,9′-acridino)heptane, and so forth; as wellas N-phenylglycine, N-phenylglycine derivatives, and so forth.

In addition to the components described hereinabove, the photosensitiveresin composition of the present embodiment preferably additionallycontains leuco crystal violet. This makes it possible to achieveadditional significant improvements in the balance betweenphotosensitivity and resolution for the photosensitive resin compositionof the present embodiment. Leuco crystal violet has the properties of aphotodye in that it develops a particular color upon absorbing light,and it is believed that leuco crystal violet accomplishes the effectcited above for it based on this property.

Viewed from the perspective of achieving this effect more effectively,the blending proportion for the leuco crystal violet in thephotosensitive resin composition of the present embodiment is preferably0.01 to 10 mass parts and more preferably 0.05 to 5 mass parts, in eachcase per 100 mass parts of the total of components (A) and (B).

In addition to the components already described above, thephotosensitive resin composition of the present embodiment mayoptionally contain other additives, e.g., dyes such as malachite greenand so forth; photodyes other than leuco crystal violet, such astribromophenyl sulfone; thermal discoloration inhibitors; plasticizerssuch as p-toluenesulfonamide and so forth; pigments; fillers; defoamers;flame retardants; stabilizers; adhesion promoters; leveling agents;stripping promoters; antioxidants; fragrances; imaging agents; andthermal crosslinkers, in each case at about 0.01 to 20 mass parts per100 mass parts of the total of components (A) and (B).

The photosensitive resin composition of the present embodiment ispreferably used to form a resist pattern by exposure to light having apeak in the wavelength range from at least 350 nm to less than 440 nm(more preferably 335 to 365 nm or 405 nm).

This light having a peak in the wavelength range from at least 350 nm toless than 440 nm may be a known light source, for example, a lightsource that effectively emits, for example, ultraviolet radiation orvisible light, such as a carbon arc lamp, mercury vapor arc lamp,high-pressure mercury lamp, xenon lamp, Ar ion laser, semiconductorlaser, and so forth.

Light sources that can be effectively used in the direct imagingtechnique described below can be exemplified by an argon gas laseremitting light at 364 nm, a solid UV laser emitting light at 355 nm, agallium nitride-type blue laser emitting light at 405 nm, and so forth.The use of the gallium nitride-type blue laser is preferred thereamongfrom the perspective of being able to more easily form the resistpattern. In addition, a digital direct exposure instrument, for example,the “DE-1AH” (trade name) from Hitachi Via Mechanics, Ltd., may also beused.

Alternatively, with regard to light sourced from a mercury lamp, forexample, a high-pressure mercury light, active light (for example, theh-line) can be used from which at least 99.5% of the light with awavelength of not more than 365 nm has been cut. A filter for cuttingthe light with a wavelength of not more than 365 nm can be exemplifiedby the SCF-100S-39L (trade name) sharp cut filter from Sigma Koki Co.,Ltd., and by the HG0405 (trade name) spectral filter from Asahi SpectraCo., Ltd.

The photosensitive resin composition as described hereinabove may becoated as a liquid resist on a metal surface, e.g., copper, a copperalloy, iron, an iron alloy, etc., and thereafter dried and then used,optionally after coating with a protective film, or it may be used forphotolithography in the form of the photosensitive element describedbelow.

A suitable embodiment of the photosensitive element of the presentembodiment is shown in FIG. 1 in schematic cross section. Thephotosensitive element 1 shown in FIG. 1 is constituted of a support 10and a photosensitive layer 14 disposed on the support 10. Thephotosensitive layer 14 comprises the photosensitive resin compositionof the present embodiment as described above.

The thickness of the photosensitive layer 14 is not particularlyrestricted, but is preferably approximately 1 to 100 μm. In addition, aprotective film may be coated on the photosensitive layer 14 on the sideF1 opposite the support 10. This protective film can be exemplified byfilms of polyethylene, polypropylene, and so forth; preferably has anadhesive strength with the photosensitive layer 14 that is less than theadhesive strength between the support 10 and the photosensitive layer14; and preferably is a low-fisheye film.

A film of, for example, polyethylene terephthalate, polypropylene,polyethylene, polyester, and so forth, can be suitably used as thesupport 10; its thickness is preferably 1 to 100 μm.

In addition to the support 10, photosensitive layer 14, and protectivefilm as described above, a protective layer and/or an intermediatelayer, e.g., a cushioning layer, adhesive layer, light-absorbing layer,gas barrier layer, and so forth, may additionally be disposed in thephotosensitive element 1.

The photosensitive element 1 can be obtained, for example, by coatingthe photosensitive resin composition on the support 10 and then dryingto form the photosensitive layer 14. Coating can be carried out by knownmethods, for example, a roll coater, comma coater, gravure coater, airknife coater, die coater, bar coater, and so forth. Drying can becarried out at 70 to 150° C. for about 5 to 30 minutes.

Coating of the photosensitive resin composition on the support 10 ispreferably optionally carried out by the application of an approximately30 to 60 mass % (as solids) solution comprising the photosensitive resincomposition dissolved in a solvent such as, for example, methanol,ethanol, acetone, methyl ethyl ketone, methyl Cellosolve, ethylCellosolve, toluene, N,N-dimethylformamide, propylene glycol monomethylether, and so forth, or in a mixed solvent of the preceding. However,the amount of residual organic solvent in the photosensitive layer afterdrying is preferably brought to 2 mass % or less in order to preventdiffusion of the organic solvent in subsequent processes.

The obtained photosensitive element 1, either as such or after theadditional lamination of the aforementioned protective film on thephotosensitive layer 14, is then, for example, wound up on a cylindricalcore and stored. This wind up is preferably carried out in such a mannerthat the support 10 faces to the outside. A plastic core can be suitablyused as the core, for example, a core of polyethylene resin,polypropylene resin, polystyrene resin, polyvinyl chloride resin, ABSresin (acrylonitrile-butadiene-styrene copolymer), and so forth.

An end separator is preferably disposed at the end surfaces of thewound-up photosensitive element roll in order to protect the endsurfaces, and a moisture-resistant end separator is preferably employedfrom the standpoint of the resistance to edge fusion. The wound-upphotosensitive element roll is preferably packaged wrapped in a blacksheet that has a low moisture permeability.

The method of the present embodiment for forming a resist patterncomprises a photosensitive layer formation step, in which aphotosensitive layer comprising the above-described photosensitive resincomposition of the present embodiment is formed on a substrate; anexposure step, in which a prescribed region of the photosensitive layeris exposed to light that has a peak in the prescribed wavelength range;and a development step, in which a resist pattern is formed bydeveloping the exposed photosensitive layer.

More specifically, the method of the present embodiment for forming aresist pattern comprises a photosensitive layer formation step, in whicha photosensitive layer comprising the above-described photosensitiveresin composition of the present embodiment is formed on a substrate; anexposure step, in which a prescribed region of the photosensitive layeris exposed to light that has a peak in the wavelength range from atleast 350 nm to less than 440 nm; and a development step, in which aresist pattern is formed by developing the exposed photosensitive layer.This method of forming a resist pattern is described in the following.

The above-described photosensitive element of the present embodiment canbe suitably used in the photosensitive layer formation step. When thephotosensitive element is employed, the protective film is removed (inthose instances where the photosensitive element has a protective film)and the photosensitive layer, while being heated to about 70 to 130° C.,is then laminated under reduced or ambient pressure onto the substrateby press-bonding at a pressure of about 0.1 to 1 MPa (about 1 to 10kgf/cm²) to form a photosensitive layer on the substrate. This substratesuitably takes the form of, for example, a copper-clad laminatecomprising copper foil disposed on one or both surfaces of a layercomprising a dielectric material such as, for example, glassfiber-reinforced epoxy resin.

In the exposure step, light (active light) is irradiated on prescribedregions of the photosensitive layer laminated on the substrate whereinthese prescribed regions correspond to the desired resist pattern. Thisexposure can be carried out by a mask exposure technique in whichexposure is carried out through a mask pattern or by a direct imagingexposure technique such as laser direct imaging exposure, DLP exposure,and so forth, wherein a direct imaging exposure technique is preferredin terms of, inter alia, resolution. Known light sources can be used asthe source of the active light, for example, light sources thateffectively emit ultraviolet radiation or visible light, such as acarbon arc lamp, mercury vapor arc lamp, high-pressure mercury lamp,xenon lamp, Ar ion laser, semiconductor laser, and so forth.

A direct imaging technique is suitably used in this embodiment from thestandpoints of high sensitivity and high resolution. Light sources thatcan be used in the direct imaging technique can be exemplified by anargon gas laser emitting light at 364 nm, a solid UV laser emittinglight at 355 nm, a gallium nitride-type blue laser emitting light at 405nm, and so forth. The gallium nitride-type blue laser is suitably usedthereamong from the perspective of being able to more easily form theresist pattern. In addition, a digital direct exposure instrument, forexample, the “DE-1AH” (trade name) from Hitachi Via Mechanics, Ltd., mayalso be used.

The use of the direct imaging technique makes it unnecessary to use aphototool to form the wiring pattern. In addition, the use of a sharpcut filter is also rendered unnecessary when the light source is a laserthat emits light at the prescribed wavelength.

The light under consideration may be light from a light source thatgenerates active light having a peak in the wavelength range from atleast 350 nm to less than 440 nm or may be light adjusted, for example,by dispersion with a filter, in such a manner that a peak is in thiswavelength range. The details of this light source are otherwise thesame as the details provided above in the description of thephotosensitive resin composition.

After exposure, the support on the photosensitive layer is removed whenthe support is present and a resist pattern is subsequently formed bydevelopment whereby the regions not subjected to photoexposure areremoved, for example, by wet development using a developing solution,for example, an aqueous alkali solution, a water-based developingsolution, organic solvent, and so forth, or by dry development. Thedevelopment method is not particularly limited, and development can becarried out by such methods as, for example, dipping, spraying,brushing, slapping, and so forth.

The aqueous alkali solution used for development can be exemplified by0.1 to 5 mass % aqueous sodium carbonate solutions, 0.1 to 5 mass %aqueous potassium carbonate solutions, 0.1 to 5 mass % aqueous sodiumhydroxide solutions, and so forth. The pH of the aqueous alkali solutionis preferably in the range from 9 to 11 and its temperature may beadjusted as appropriate in response to, for example, the solubility ofthe photosensitive layer. A surfactant, defoamer, organic solvent, andso forth may also be added to the aqueous alkali solution. The resinforming the resist pattern may as necessary be subjected to additionalcuring after the development step but prior to the formation of theconductor pattern; this additional curing may be effected by heating atabout 60 to 250° C. or by photoexposure to about 0.2 to 10 J/cm².

In the method of the present embodiment for producing a printed wiringboard, a printed wiring board is formed through a conductor patternformation step in which a conductor pattern is formed on theaforementioned substrate based on the resist pattern formed as describedabove. The conductor pattern is formed by using the developed resistpattern as a mask and treating the unmasked, exposed copper foil regionsby a known method, for example, etching, plating, and so forth. Theplating method can be exemplified by copper plating, solder plating,nickel plating, gold plating, and so forth. Etching can be carried outusing, for example, a cupric chloride solution, ferric chloridesolution, basic etching solution, and so forth. The application of thesemethods enables the formation of a conductor pattern by the selectiveformation of a conductor layer in the trench regions (exposed regions ofthe substrate) in the resist pattern. Or, conversely thereto, aconductor layer can be selectively formed in those regions protected bythe photosensitive layer that remains post-development.

After the etching or plating treatment, the photosensitive layer formingthe resist pattern is stripped off, for example, using an aqueoussolution more strongly alkaline than the alkali aqueous solution usedfor development, thus yielding a printed wiring board on which aspecified conductor pattern has been formed. The strongly basic aqueoussolution can be exemplified by a 1 to 10 mass % aqueous sodium hydroxidesolution, a 1 to 10 mass % aqueous potassium hydroxide solution, and soforth. The technique used to strip off the photosensitive layer can beexemplified by immersion, spraying, and so forth.

Printed wiring boards, for example, multilayer printed wiring boardshaving small-diameter through holes, can be suitably produced using theproduction method described hereinabove.

Suitable embodiments of the present invention are described above, butthe present invention is not limited to the preceding embodiments.

EXAMPLES

The present invention is described in additional detail by the examplesthat follow, but the present invention is not limited to these examples.

Examples 1 to 7 and Comparative Examples 1 and 2 Preparation ofPhotosensitive Resin Composition Solutions

The starting materials shown in Table 1, the component (C1) shown inTable 2 or 3, and the 4,4′-bis(diethylamino)benzophenone shown in Table3 (abbreviated as EAB in Table 3) were intermixed to uniformity in theamounts shown in the respective tables to prepare solutions ofphotosensitive resin compositions according to Examples 1 to 7 andComparative Examples 1 and 2. The following were used as component (C1):1-phenyl-3-(4-methoxystyryl)-5-(4-methoxyphenyl)pyrazoline (abbreviatedas PYR-M in Table 2),1-phenyl-3-(4-isopropylstyryl)-5-(4-isopropylphenyl)pyrazoline(abbreviated as PYR-I in Table 2), and1-phenyl-3-(4-tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline(abbreviated as PYR-B in Table 3).

A higher solubility in solvent is desirable for the PYR-M, PYR-I, andPYR-B from the standpoint of bringing about a better balance between thesensitivity and resolution. A high solubility also facilitatespreparation of the photosensitive resin composition solution and thusprovides an excellent workability. The solubility of PYR-M, PYR-I, andPYR-B in 100 mL toluene solvent at 23° C. is shown in Table 4.

TABLE 1 Blending quantity Starting material (g) Component (A)2-methoxyethanol/toluene solution 54 of methacrylic acid/methyl (solids)methacrylate/styrene (25/50/25 weight ratio, weight-average molecularweight: 55,000), acid number of the solids fraction: 163.1 mg KOH/gComponent (B) EO-modified, bisphenol A skeleton 46 dimethacrylateComponent (C2) 2,2′-bis(o-chlorophenyl)-4,5-4′,5′- 3.7tetraphenyl-1,2′-biimidazole Color former leuco crystal violet (LCV) 0.5Dye malachite green (MKG) 0.03 Solvent acetone 10 toluene 7N,N-dimethylformamide 3 methanol 3

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Component PYR-M 0.2 0.5 0.8— — — (C1) addition (g) PYR-I — — — 0.2 0.5 0.8 addition (g) Thicknessof the 25 25 25 25 25 25 photosensitive layer (μm) OD value 365 nm 0.520.73 1.00 0.48 0.68 1.00 (absorbance) 405 nm 0.53 0.77 1.00 0.49 0.701.00 Sensitivity (mJ/cm²) 66 51 40 68 52 39 Resolution ST = 15 16 16 1515 16 (μm) 14/41 ST = 15 16 18 15 16 18 17/41 ST = 16 18 18 15 18 1820/41

TABLE 3 Comp. Ex. 1 Comp. Ex. 2 Example 7 PYR-B addition (g) — — 0.2 EABaddition (g) — 0.4 — Thickness of the 25 25 25 photosensitive layer (μm)OD value 365 nm 0.21 1.70 0.44 (absorbance) 405 nm 0.13 0.52 0.45Sensitivity (mJ/cm²) 557 120 95 Resolution (μm) ST = 14/41 16 20 15 ST =17/41 18 18 16 ST = 20/41 20 20 20

TABLE 4 PYR-M PYR-I PYR-B Solubility (g) 3 20 5.2

<The Photosensitive Element>

The solutions prepared as described above of the photosensitive resincompositions of Examples 1 to 7 and Comparative Examples 1 and 2 wereuniformly coated on 16 μm-thick polyethylene terephthalate films. Thecoated solution (film coating) was then dried for 10 minutes at 70° C.and 10 minutes at 100° C. using a hot-wind convection drier to give aphotosensitive element in which a photosensitive layer comprising theaforementioned photosensitive resin composition was disposed on one sideof the polyethylene terephthalate film functioning as a support. Thefilm thickness of the photosensitive layer was 25 μm.

The optical density (OD value) of the photosensitive layer as a functionof the incident light wavelength was measured using a UVspectrophotometer (a U-3310 spectrophotometer from Hitachi). The UVabsorption spectrum was obtained by carrying out continuous measurementfrom 550 nm to 300 nm in absorbance mode using as reference the sametype of polyethylene terephthalate film as used for the support; thevalue of the absorbance at 365 nm and 405 nm was used as the OD value atthese wavelengths. The UV absorption spectra are shown in FIG. 2. In thefigure, (c1) refers to the UV absorption spectrum for Example 1; (c2)refers to the UV absorption spectrum for Example 4; and (c3) refers tothe UV absorption spectrum for Example 7. The (c2) and (c3) spectra inFIG. 2 are almost superimposed on one another in the wavelength range ofapproximately 340 to 420 nm. The absorbance in Examples 4 and 7 forincident light at 365 nm was 0.48 and 0.44, respectively, and forincident light at 405 nm was 0.49 and 0.45, respectively. The wavelengthof maximum absorption (wavelength at which the absorbance passes througha maximum) in Example 1 (PYR-M), Example 4 (PYR-I), and Example 7(PYR-B) was 385.2 nm, 386.2 nm, and 387.2 nm, respectively.

<Resist Pattern Formation>

A two-sided copper-clad laminate (MCL-E-67 (product name) from HitachiChemical Co., Ltd.) was prepared; this two-sided copper-clad laminatehad copper foil (thickness 35 μm) laminated on both sides of a glassfiber-reinforced epoxy resin layer. The copper surface of this laminatewas polished with a polisher (Sankei Co., Ltd.) fitted with a brushequivalent to #600 and was thereafter washed with water and dried in anair current. Then, while the two-sided copper-clad laminate was beingheated to 80° C., the photosensitive element obtained as described abovewas pasted thereon in such a manner that its photosensitive layer sidewas adhered to the copper foil surfaces; this was followed by pressingat 0.4 MPa while heating to 120° C. Cooling to 23° C. then yielded alaminate comprising the photosensitive layer disposed on both surfacesof the two-sided copper-clad laminate.

The following were then laid in the sequence given on the surface of thepolyethylene terephthalate film that was disposed as the outermost layerof the laminate: a phototool provided with a 41-step tablet and, as anegative for evaluation of the resolution, a phototool provided with awiring pattern that had line width/space width=6/6 to 35/35 (unit: μm).The 41-step tablet on the phototool had a density range of 0.00 to 2.00and a density step of 0.05; the tablet (rectangle) had a size of 20mm×187 mm, and each step (rectangle) had a size of 3 mm×12 mm. An HG0405(product name) spectral filter (bandpass filter that transmits lightwith a wavelength of 405 nm±30 nm) from Asahi Spectra Co., Ltd., wasthen placed on top of this stack.

This assembly was exposed, using a parallel light exposure instrumenthaving a 5 kW short arc lamp as its light source (product name:EXM-1201, from Orc Manufacturing Co., Ltd.), to light in an amount suchthat the number of remaining steps after development of the 41-steptablet was 14, 17, or 20. The sensitivity was defined as the amount oflight exposure at which the number of remaining steps after developmentof the 41-step tablet was 17. The irradiance of the light transmittedthrough the bandpass filter was measured using an accumulating UV lightmeter and a detector, and the amount of light exposure was defined asirradiance×exposure time. A UIT-150-A (product name, from Ushio Inc.,also usable as an irradiance meter) was used as the accumulating UVlight meter and a UVD-S405 (product name, sensitivity wavelength region:320 nm to 470 nm, wavelength for calibrating absolute value: 405 nm) wasused as the detector.

The polyethylene terephthalate film was then removed and development wascarried out by spraying the uncovered photosensitive layer for 24seconds at 30° C. with a 1.0 weight % aqueous sodium carbonate solutionto remove those regions that had not been exposed to light. Theresolution was defined as the smallest value of the line-to-line spacewidth at which the regions not exposed to light could be cleanlyremoved, the lines did not meander, and void-free lines were produced.For the resolution and sensitivity as herein defined, smaller numericalvalues are indicative of better values.

The results of the above-described evaluations carried out on thephotosensitive resin compositions of Examples 1 to 7 and ComparativeExamples 1 and 2 are shown in Tables 2 and 3.

Examples 8 to 13 and Comparative Example 3

Solutions of the photosensitive resin compositions according to Examples8 to 13 and Comparative Example 3 were prepared by mixing the startingmaterials shown in Table 5, the component (C1) shown in Table 6, andleuco crystal violet to homogeneity using the amounts shown in thetables. 1-phenyl-3-(tert-butylstyryl)-5-(4-tert-butylphenyl)pyrazoline(PYR-B in Table 3, Nippon Chemical Industrial Co., Ltd.) was used ascomponent (C1). The maximum absorption wavelength λ_(max) of thispyrazoline derivative (wavelength of maximum absorbance) was 387.2 nm.

TABLE 5 Blending quantity Starting material (g) Component (A)2-methoxyethanol/toluene solution 54 of methacrylic acid/methyl (solids)methacrylate/styrene (25/50/25 weight ratio, weight-average molecularweight: 55,000), acid number of the solids fraction: 163.1 mg KOH/gComponent (B) EO-modified, bisphenol A skeleton 46 dimethacrylateComponent (C2) 2,2′-bis(o-chlorophenyl)-4,5-4′,5′- 3.7tetraphenyl-1,2′-biimidazole Dye malachite green (MKG) 0.03 Solventacetone 10 toluene 7 N,N-dimethylformamide 3 methanol 3

TABLE 6 Example Example Example Example Example Example Comp. 8 9 10 1112 13 Example 3 Blending 0.30 0.50 0.70 0.25 0.25 0.25 — quantity ofcomponent (C1) (g) Blending 0.30 0.30 0.30 0.30 0.50 1.0 0.30 quantityof leuco crystal violet addition (g) Thickness of 25 25 25 25 25 25 25the photosensitive layer (μm) OD 365 nm 0.673 0.998 1.229 1.202 0.5040.515 0.063 value 405 nm 0.725 1.183 1.482 1.221 0.570 0.586 0.107(absorbance) Sensitivity 94 71 63 83 83 75 557 (mJ/cm²) Resolution ST =18 25 25 14 18 16 35 (μm) 14/41 ST = 16 18 20 16 20 18 30 17/41 ST = 1618 20 16 25 20 30 20/41

<The Photosensitive Element>

The solutions of the photosensitive resin compositions according toExamples 8 to 13 and Comparative Example 3 prepared as described abovewere uniformly coated on 16 μm-thick polyethylene terephthalate film.The coated solution (coated film) was then dried for 10 minutes at 70°C. and 10 minutes at 100° C. using a hot-wind convection drier to give aphotosensitive element in which a photosensitive layer comprising thephotosensitive resin composition was disposed on one side of thepolyethylene terephthalate film functioning as a support. The filmthickness of the photosensitive layer was 25 μm.

The optical density (OD value) of the photosensitive layer as a functionof the incident light wavelength was measured as in Examples 1 to 7 andComparative Examples 1 and 2 using a UV spectrophotometer (a U-3310spectrophotometer from Hitachi). The UV absorption spectra are shown inFIGS. 3 to 6. (a1) refers to the UV absorption spectrum for Example 8;(a2) refers to the UV absorption spectrum for Example 9; (a3) refers tothe UV absorption spectrum for Example 10; (a4) refers to the UVabsorption spectrum for Example 11; (a5) refers to the UV absorptionspectrum for Example 12; (a6) refers to the UV absorption spectrum forExample 13; and (b1) refers to the UV absorption spectrum forComparative Example 3.

<Resist Pattern Formation>

Proceeding as in Examples 1 to 7 and Comparative Examples 1 and 2, alaminate in which the photosensitive layer was disposed on both sides ofthe two-sided copper-clad laminate was first obtained. Then, againproceeding as in Examples 1 to 7 and Comparative Examples 1 and 2, thefollowing were laid in the sequence given on the surface of thepolyethylene terephthalate film that was disposed as the outermost layerof the laminate: a phototool provided with a 41-step tablet and aphototool provided with a prescribed wiring pattern. An HG0405 (productname) spectral filter (bandpass filter that transmits light with awavelength of 405 nm±30 nm) from Asahi Spectra Co., Ltd., was thenplaced on top of this stack.

This assembly was exposed to light as in Examples 1 to 7 and ComparativeExamples 1 and 2. The sensitivity was defined as the amount of lightexposure at which the number of remaining steps after development of the41-step tablet was 17. The irradiance of the light transmitted throughthe bandpass filter was measured as before using an accumulating UVlight meter and a detector, and the amount of light exposure was definedas irradiance×exposure time.

The polyethylene terephthalate film was then removed and development wascarried out by spraying the uncovered photosensitive layer for 24seconds at 30° C. with a 1.0 weight % aqueous sodium carbonate solutionto remove those regions that had not been exposed to light. Theresolution was defined as the smallest value of the line-to-line spacewidth at which the regions not exposed to light could be cleanlyremoved, the lines did not meander, and void-free lines were produced.For the resolution and sensitivity as herein defined, smaller numericalvalues are indicative of better values.

The post-development resist shape was inspected using an S-500A scanningelectron microscope from Hitachi. It is desirable for the resist to havean approximately rectangular shape.

The results of the above-described evaluations carried out on thephotosensitive resin compositions of Examples 8 to 13 and ComparativeExample 3 are shown in Table 6.

INDUSTRIAL APPLICABILITY

The present invention provides a photosensitive resin composition thathas the ability to form a resist pattern by direct imaging exposure andto do so at a satisfactory sensitivity and resolution; the presentinvention also provides a photosensitive element that uses thisphotosensitive resin composition, a method of forming a resist patternusing this photosensitive resin composition, and a method of producing aprinted wiring board using this photosensitive resin composition.

1. A method of forming a resist pattern, comprising: forming aphotosensitive layer comprising a photosensitive resin composition on asubstrate, wherein the photosensitive resin composition comprises: (A) abinder polymer; (B) a photopolymerizable compound that has anethylenically unsaturated bond; (C1) a compound represented by generalformula (1) below,

wherein, at least one R represents a C₄₋₁₂ alkyl group; the sum of a, b,and c is 1 to 6; and when the sum of a, b, and c is 2 to 6, each R maybe the same as or different from one another; and (C2) a2,4,5-triarylimidazole dimer or a derivative thereof, wherein thecontent of the component (C1) is 0.05 to 0.8 mass parts per 100 massparts of the total content of components (A) and (B), and the content ofthe component (C2) is 3 to 5 mass parts per 100 mass parts of the totalcontent of components (A) and (B) exposing prescribed regions of thephotosensitive layer to light by a direct exposure imaging technique;and developing the exposed photosensitive layer to form a resistpattern.
 2. The method of forming a resist pattern according to claim 1,wherein component (A) comprises an acrylic-type polymer that has asconstituent units thereof a monomer unit derived from acrylic acidand/or methacrylic acid and a monomer unit derived from alkyl ester ofacrylic acid and/or alkyl ester of methacrylic acid.
 3. The method offorming a resist pattern according to claim 1, wherein the content ofthe component (B) is 20 to 80 mass parts per 100 mass parts of the totalcontent of components (A) and (B).
 4. The method of forming a resistpattern according to claim 1, wherein the sum of a, b, and c is 1 or 2.5. The method of forming a resist pattern according to claim 1, whereinsaid direct exposure imaging technique includes exposure to laser lighthaving a peak in the wavelength range from at least 350 nm to less than440 nm.
 6. A method of producing a printed wiring board, comprising:performing the method of forming a resist pattern according to claim 1;and forming a conductor pattern on the substrate based on said resistpattern.
 7. The method of forming a resist pattern according to claim 1,wherein the component (C2) is at least one selected from the groupconsisting of 2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer,2-(o-fluorophenyl)-4,5-diphenylimidazole dimer,2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer, and2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer.
 8. The method offorming a resist pattern according to claim 1, wherein thephotosensitive resin composition further includes (D) leuco crystalviolet.
 9. The method of forming a resist pattern according to claim 8,wherein the leuco crystal violet is included in an amount of 0.05 to 5mass parts per 100 mass parts of the total of components (A) and (B).10. The method of forming a resist pattern according to claim 1, whereina weight-average molecular weight of component (A) of the photosensitiveresin composition is 40000 to 80000.